Yii2 rest api getBodyParams() can't get params load(Yii::$app->getRequest()->getBodyParams(), ''); from react native post

How can I get param from Post react native? Post react native I try here to send some data to the request yii:

    let  body =  {
                demande_title:demande_title,
                created_Date:created_Date,
                updated_Date:updated_Date,
                demande_Type:demande_Type,
                demande_Action:demande_Action,
                demande_status:demande_status,
                demande_content:demande_content,
                demande_color:demande_color,
                utf_utilisateur_front_id:1

            };
            let response = await fetch(url, {
                method: "POST",
                headers: {
                    Authorization: `Bearer ${getState().auth.token}`,
                    "Content-Type": "application/json",
                },
                body: JSON.stringify(body),
            });
if (!response.ok) {
                throw new Error("Something went wrong !");
            }

I want to get data with yii load param and insert(create new demand) in data base . Code Yii :

 public function actionDemandeCreate()
{
    $demande = new Demande(); 
    $demande->load(Yii::$app->getRequest()->getBodyParams(), '');
    if ($demande->save()) {
        Yii::$app->response->statusCode = 201;
        return [
            'demande_id'=>$demande->id,
            'demande_title'=>$demande->demande_title,
            'created_Date'=>$demande->created_Date,
            'updated_Date'=>$demande->updated_Date,
            'demande_Type'=>$demande->demande_Type,
            'demande_color'=>$demande->demande_color,
            'demande_Action'=>$demande->demande_Action,
            'demande_status'=>$demande->demande_status,
            'demande_content'=> $demande->demande_content,
        ];
    } else {
        Yii::error($demande->getErrors(), __METHOD__);
        throw new ServerErrorHttpException('Une erreur s\'est produite lors de la création. Merci de réessayer.');         
}
}

i have error with response: Error : Something went wrong